Measurement of the mechanics of respiration in guinea pigs is used as a bioassay method for the assessment of irritant potency. Currently we are working with oil mists and sulfur dioxide. We plan during the next year to examine the response to sulfites, including sodium sulfite and sodium bisulfite. We plan to have determinations made of whether or not sulfite can be detected in the aerosols of copper salts which were potent potentiators of sulfur dioxide. We have completed a study of the effect of combinations of ozone and sulfur dioxide. In the guinea pigs the response to the combination was essentially that observed with ozone alone. We could detect no response which could be attributed to sulfuric acid formed from a possible oxidation of sulfur dioxide by ozone.